As for any calligraphic reference by a third hand directly connected to the painting, an inscription on the painting or its box, a letter of reference, it should be treated as an individual artwork. It only could have any value after we could establish its authenticity, but not a very great one. Even a great mind might be wrong with the honest inscription. A piece of paper could be moved easily, a box exchanged without a problem.

With a toolset of  evaluating quality, understanding brushstrokes as individual hand writing and questioning composition in its originality and its historical context, good references to compare to, authentication is reliably possible.
Often the situation is much less obvious and only a meagre result like “It might be …” or “we cant say” is achievable. Because for instance we do not have the appropriate references in this case.
But in the end it is always much better to admit this, than pretending to know more while having no real clue.

Authentication could only be achieved seriously with arguments. It has to be understandable.

Unfortunately it is so much easier to sell authority than to create a stringent set of understandable arguments.

Unfortunately!